This invention relates to vaso-occlusive devices, such as vaso-occlusive coils and the like, for the embolization of vascular aneurysms and similar vascular abnormalities. Specifically, the invention is an improvement over existing two layer or two element coaxial vaso-occlusive devices, particularly those having a polymer coating or covering. In particular, the present invention is a three layer or three element coaxial vaso-occlusive device that provides improved durability, pushability, and trackability inside a microcatheter. The characteristic termed “trackability” relates to the ease of advancing one interventional device within or over another, and it is related to friction and flexibility.
Vaso-occlusive devices are typically used within the vasculature of the human body to block the flow of blood through a vessel through the formation of an embolus. Vaso-occlusive devices are also used to form an embolus within an aneurysm stemming from the vessel. Vaso-occlusive devices can be formed of one or more elements, generally delivered into the vasculature via a catheter or similar mechanism.
The embolization of blood vessels is desired in a number of clinical situations. For example, vascular embolization has been used to control vascular bleeding, to occlude the blood supply to tumors, and to occlude vascular aneurysms, particularly intracranial aneurysms. In recent years, vascular embolization for the treatment of aneurysms has received much attention. Several different treatment modalities have been employed in the prior art. One approach that has shown promise is the use of thrombogenic microcoils. These microcoils may be made of a biocompatible metal alloy (typically platinum and tungsten) or a suitable polymer. If made of metal, the coil may be provided with Dacron fibers to increase thrombogenicity. The coil is deployed through a microcatheter to the vascular site. Examples of microcoils are disclosed in the following U.S. Pat. No. 4,994,069—Ritchart et al.; U.S. Pat. No. 5,133,731—Butler et al.; U.S. Pat. No. 5,226,911—Chee et al.; U.S. Pat. No. 5,312,415—Palermo; U.S. Pat. No. 5,382,259—Phelps et al.; U.S. Pat. No. 5,382,260—Dormandy, Jr. et al.; U.S. Pat. No. 5,476,472—Dormandy, Jr. et al.; U.S. Pat. No. 5,578,074—Mirigian; U.S. Pat. No. 5,582,619—Ken; U.S. Pat. No. 5,624,461—Mariant; U.S. Pat. No. 5,645,558—Horton; U.S. Pat. No. 5,658,308—Snyder; and U.S. Pat. No. 5,718,711—Berenstein et al.
A specific type of microcoil that has achieved a measure of success is the Guglielmi Detachable Coil (“GDC”), described in U.S. Pat. No. 5,122,136—Guglielmi et al. The GDC employs a platinum wire coil fixed to a stainless steel delivery wire by a solder connection. After the coil is placed inside an aneurysm, an electrical current is applied to the delivery wire, which electrolytically disintegrates the solder junction, thereby detaching the coil from the delivery wire. The application of the current also creates a positive electrical charge on the coil, which attracts negatively-charged blood cells, platelets, and fibrinogen, thereby increasing the thrombogenicity of the coil. Several coils of different diameters and lengths can be packed into an aneurysm until the aneurysm is completely filled. The coils thus create and hold a thrombus within the aneurysm, inhibiting its displacement and its fragmentation.
The advantages of the GDC procedure are the ability to withdraw and relocate the coil if it migrates from its desired location, and the enhanced ability to promote the formation of a stable thrombus within the aneurysm.
A more recent development in the field of microcoil vaso-occlusive devices is exemplified in U.S. Pat. No. 6,299,619—Greene, Jr. et al. and U.S. Pat. No. 6,602,261—Greene, Jr. et al., both assigned to the assignee of the subject invention. These patents disclose vaso-occlusive devices comprising a microcoil with one or more expansile elements disposed on the outer surface of the coil. The expansile elements may be formed of any of a number of expansile polymeric hydrogels, or alternatively, environmentally-sensitive polymers that expand in response to a change in an environmental parameter (e.g., temperature or pH) when exposed to a physiological environment, such as the blood stream.
While the microcoils with expansile elements have exhibit great promise in, for example, embolizing aneurysms of a wide variety of sizes and configurations, the expansile elements increase the frictional forces between the vaso-occlusive device and a microcatheter through which the device is deployed. Furthermore, depending on the configuration and material of the expansile elements, the flexibility of the device may be reduced. These factors may result in a device that has less than optimal pushability (resistance to buckling) and reduced trackability (as defined above).
There has thus been a long-felt, but as yet unsatisfied need for a microcoil vaso-occlusive device that has all the advantages of the expansile element type of device, and that also exhibits enhanced pushability and trackability, with good durability characteristics.